For "cloned-mac-address", the empty string "" is an invalid
value that is rejected by verify().
Commit 8eed671 changed how the property is serialized to D-Bus.
Before, it was serialized using _nm_utils_hwaddr_to_dbus().
For invalid or empty addresses, this would not serialize the
value on D-Bus (or before commit 76aa6f8e0, it would create
a bogus value with no array elements).
With commit 8eed671, the cloned-mac-address gets also serialized
as "assigned-mac-address" via _nm_utils_hwaddr_cloned_data_synth(),
which would pass on invalid strings that the server would then reject.
That breaks for example nmtui. Try editing a connection with
"cloned-mac-address" set to NULL. Note, as long as you don't edit
the cloned MAC address in nmtui, you can save the modification.
Once you start modifying the entry, you can no longer set an empty
MAC address as the server now receives the invalid empty string.
Thus, the "OK" button fails with
Unable to save connection:
802-3-ethernet.cloned-mac-address:
is not a valid MAC address
It also means, nmtui cannot modify the "cloned-mac-address" field to
become empty.
Fix that problem at various places by coercing "" to NULL.
Fixes: 8eed67122chttps://bugzilla.redhat.com/show_bug.cgi?id=1372799
814784aa46